Referring to FIGS. 1–4, a conventional parking meter 200, such as Duncan Models 80, 90, 95, 2000, 90 duplex and 95 duplex, has an upper housing 202 for receiving coins, using a timer and displaying a time period based on the amount and type of coins received. The meter 200 also has a lower housing or vault 204 typically holding a coin box (not shown) for storing the coins inserted into the top housing 202. The vault 204 has an opening 206 covered by a vault door 208 that swings on brackets 210 for opening and closing the vault door. A lock cylinder 212 is positioned on a back or back side 214 of the door 208 and has a key hole 216 exposed to the exterior of the door 208 through a hole 218 in the door. 
The lock cylinder 212 has a rotatable shaft 242 secured to a lock cam 220 which has two slots 222 for receiving bolt pins 224 extending from bolts 226. The bolts 226 are supported between bracket plates 228, 230. When a key (not shown) is turned in the lock cylinder 212, it turns the lock cam 220 which pushes the bolt pins 224 along slots 222. This in turn drives the bolts 226 to engage or disengage holes 232 on bolting plates 234 disposed on the vault housing 204 in order to lock or unlock the vault door 208. 
As shown in FIG. 3, a retainer 236 straddles the lock cylinder 212 and clamps onto the top and sidewalls 238 of the lock cylinder to prevent rotation of the body or exterior surface 244 of the lock cylinder, as well as secure it against the door 208 both vertically and horizontally. Walls 240 of the bracket 228 abut the sides of the retainer 236 and prevent rotation of the retainer. 
Frequently, the lock cylinder 212 breaks or malfunctions so that the vault door 204 cannot be opened. This occurs, for example, when the wear of the gears  in the lock cylinder or a broken key piece or other foreign instrument within the keyhole jams the lock cylinder so that shaft 242 will not rotate. In this case, the vault door must be opened first to gain access to the lock cylinder 212 for replacement or repair. One way to unlock the door is to rotate the entire lock cylinder (or lock cylinder body) 212 to thereby rotate the cam 220 which in turn moves the bolts 226. This cannot be accomplished, however, as long as the retainer 236 is holding the lock cylinder 212 and prevents such rotation. 
As a result, opening the broken vault door 208 is typically accomplished by drilling holes at appropriate locations on the vault door as known in the art to disengage it from the vault housing 204. Once the door 208 is open, the retainer 236 can be pulled off of the lock cylinder 212 to remove it from the door 208. This procedure not only requires repeated use of expensive and sometimes dangerous equipment (i.e. drills), but frequently damages the vault door 208, bracket plates 228, 230 and other pieces of the lock on the door. In that case, repair and replacement of these additional parts becomes necessary when, initially, only the lock cylinder was broken. 
Another problem occurs once the retainer is pulled off and the lock cylinder is free to rotate and move. In that case, if the lock cam 220 moves outward (i.e. away from the vault door 208) so that it disengages from the bolt pins 224, the lock cylinder 212, along with the lock cam 220, will fall into the interior of the vault 204. It is frequently cumbersome and time consuming to retrieve the lock cylinder and cam from inside the vault.  